Air-conditioning apparatuses are used to create in the air-conditioned rooms comfortable conditions of occupation at any time of year, as they hold the temperature and humidity of the room air within fixed limits' and provide for a sufficient ventilation with fresh air.
In winter the supply air temperature is higher than the room air temperature when the air is also meant to warm the room, and in summer the supply air is injected at a lower temperature in order to hold the room at the desired cooled room air temperature.
Ordinarily, to achieve this, a conventional air-conditioning apparatus circulates too high an amount of air, the temperature of which has been adapted to the heating and cooling requirement. This is regarded as disadvantageous as a large volume of air is circulated even after the desired temperature has already been reached. Moreover, the danger exists that the supply air will be blown into the room through the supply air channel and will immediately leave the room to be air-conditioned through the exhaust air channel. There takes place very little mixing of the new supply air with the air present in the room.
Further, when air-conditioning several rooms, there is the problem that different desired temperatures are sought in the different rooms. An adaptation of the temperatures which takes into consideration the comfort in each room is possible only with difficulty.